Method for frequency regulation of tuning-fork vibrator

ABSTRACT

For regulating the vibration frequency of a tuning-fork vibrator to a desired frequency, the tuning-fork vibrator is regulated so that its vibration frequency may become a frequency lower than the desired frequency by a predetermined value, and then the tuning-fork vibrator is regulated so that a difference between proper vibration frequencies of both legs of the vibrator may become smaller than a predetermined value, and further, the vibrator is regulated so that the desired frequency may be reached, while maintaining the difference in the proper vibration frequency smaller than the predetermined value. In this way, the desired frequency can rapidly be attained.

TECHNICAL FIELD

The present invention relates to a method for regulating the frequencyof a piezo-electric tuning-fork vibrator.

TECHNICAL BACKGROUND

A tuning-fork vibrator, produced by cutting a piezo-electric materialsuch as, for example, a crystal into a tuning fork configuration, maysometimes be incorporated in an oscillation circuit for obtaining areference signal. Such a tuning-fork vibrator is usually mounted bysupporting its base portion. When proper vibration frequencies of thetwo legs of the tuning fork are not equal to each other, that is, whenthey are not in equilibrium, a leakage oscillation develops in the baseportion and if the base portion is supported with the vibrationfrequencies left unbalanced, the vibration frequency of the tuning forkdeviates from its original vibration frequency and its Q is degraded. Toavoid this, the tuning-fork vibrator has heretofore been supportedsoftly to avert the influence of the support of the vibrator on itsvibration frequency. Accordingly, when the tuning-fork vibrator isincorporated, for example, in a moving member, it has been difficult toobtain a support structure which supports the vibrator sufficiently evenwhen subjected to a mechanical shock.

In view of the above, it has been proposed to correct imbalance of thevibration of the tuning-fork vibrator to thereby stabilize itsvibration. With this method, since a leakage vibration develops in thebase portion of the tuning-fork vibrator when its vibration isunbalanced, that is, when the proper vibrations of both legs are not inequilibrium, the leakage vibration is measured and, from an increase ordecrease in the leakage vibration in the base portion, it is calculatedpredictively as to which one of the legs should be ground and how much,and then, based on the calculation results, grinding is conducted tobring the proper vibrations of both legs into agreement with each other.

The vibration frequency of the tuning-fork vibrator can be controlled byselecting the lengths of its legs; in general, the legs are formed inadvance longer than a value which would yield a frequency desired toobtain and then the legs are ground shorter to approach the desiredfrequency. By the way, it is the general practice in the prior art towork the legs of the tuning-fork vibrator so that their proper vibrationfrequencies may be equal to each other or in equilibrium, that is, noleakage vibration may occur in the base portion and then to grind theboth legs an equal length, thereby obtaining the desired frequency. Inthe case of such frequency regulation, if the proper vibration frequencyof the vibrator prior to the working appreciably deviates from thedesired frequency, even when the legs are correctly worked to reach theequilibrium state first and then they are each ground accurately by thesame length, it may often happen, in practice, that the vibrator thusworked becomes unbalanced. The reason is that this method is based onthe assumption that the vibrator is uniform all over and when theuniformity is lost, even if slightly, the equilibrium is destroyed inthe process of making the vibration frequency of the vibrator approachthe desired frequency after the equilibrium working.

In contrast to the foregoing, it has been considered to cut out atuning-fork vibrator in a configuration which has an oscillationfrequency as close to the desired frequency as possible and then subjectit to equilibrium working to make the vibration frequency furtherapproach the desired frequency. To perform this, it is necessary to cutout the vibrator so that its vibration frequency may be very close tothe desired frequency but this requires a very high degree of accuracy;otherwise, the vibration frequency would become higher than thefrequency desired to obtain, resulting in no frequency regulationbecoming possible. Accordingly, in view of the actual manufacturingtechniques that are presently available, it is not practical in terms ofproductivity and manufacturing costs to cut out first, with such highaccuracy, a tuning-fork vibrator having a vibration frequency close tothe desired frequency.

Further, it can also be considered to make the vibration frequency ofthe vibrator approach the desired frequency by performing theequilibrium working first and then checking whether the desiredfrequency is reached and, if not, effecting the equilibrium workingagain; but this method is defective in that the working time is long.

An object of the present invention is to provide a method for thefrequency regulation of a tuning-fork vibrator by which the vibrator iscut out relatively simply so that its vibration frequency may beappreciably lower than a desired frequency and by which the tuning-forkvibrator can be adjusted correctly to the desired frequency andwell-balanced.

DISCLOSURE OF THE INVENTION

According to the present invention, the vibration frequency of atuning-fork vibrator to be regulated is measured first and both of itslegs are equally worked until the vibration frequency becomes higherthan a frequency which is lower than a desired frequency by apredetermined value, and then the legs are subjected to equilibriumworking so that the amount of vibration of the base portion of thevibrator, that is, a leakage vibration may be reduced. The vibratorsubjected to such equilibrium working is worked, with variations in theamount of vibration of the base portion held smaller than apredetermined value. As described above, the vibrator is worked first sothat its vibration frequency may be raised from a relatively lowfrequency to a frequency a little lower than the desired frequency, thatis, increased above a certain reference frequency; in this way, theabovesaid reference frequency is rapidly approached by working which iscommon to the both legs and relatively rough. Then the equilibriumworking is performed and thereafter the desired frequency is graduallyapproached. Accordingly, since the difference between the desiredfrequency and the reference frequency is small, there is no fear thatthe equilibrium state will be destroyed during the equilibrium workingsteps used for approaching the desired frequency.

That a difference between individual proper vibration frequencies of thelegs of the tuning-fork vibrator has become smaller than a predeterminedvalue is detected by existence of a condition wherein a differencebetween the vibration frequency of the tuning-fork vibrator when itsbase portion is mechanically restrained and the vibration frequency whenthe base portion is released from such mechanical restraint becomessmaller than a predetermined value. Further, for detecting that theproper vibration frequencies of both legs have been brought into theequilibrium state, that is, the difference therebetween has been reducedto a value smaller than the predetermined value, the difference betweenthe proper vibration frequencies is measured after working of each legof the tuning-fork vibrator and the measured value is compared with apreviously measured value; when the current value is smaller than theprevious value, the leg that was worked latest is worked again and whenthe current value is larger than the previous value, the other leg isworked. Such operations are repeated until it is detected that thedifference in the proper vibration frequency between the legs becomessmaller than the predetermined value, whereby to establish theequilibrium state. Alternatively, a minimum value of the difference inthe proper vibration frequency is detected by similar operations toprovide the equilibrium state, or a count is taken of the number oftimes of switching the working between the two legs and the state inwhich the count value exceeds a predetermined value is regarded as theequilibrium state.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a tuning-fork vibrator; FIG. 2diagrammatically illustrates an apparatus for working the tuning-forkvibrator;

FIG. 3 is a block diagram of an electrical arrangement of the vibratorfrequency regulating apparatus of the present invention;

FIG. 4 is a block diagram illustrating a detailed example of theelectrical arrangement of the apparatus of the present invention;

FIG. 5 is a graph showing variation characteristics of Δf;

FIG. 6 is a diagram showing the external appearance of an example of anautomatic vibrator grinding apparatus;

FIG. 7 is a sectional view of a specific example of FIG. 6;

FIG. 8 is a sectional view taken on the line A--A in FIG. 7;

FIG. 9 is a diagram showing a part of a section on the line B--B in FIG.7;

FIG. 10 is a diagram showing an example of a vibrator driving portion ofa support structure;

FIG. 11 is an enlarged sectional view of a rotary box;

FIG. 12 is a sectional view showing a vibrator mounted on a support;

FIG. 13 is a block diagram illustrating an example of a device formeasuring which one of legs of the vibrator is larger in propervibration than the other; and

FIG. 14 is a diagram showing the relationships between the legs of thevibrator and a slit 149.

MOST PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 shows a tuning-fork vibrator made of a piezo-electric materialsuch, for example, a crystal, and its pair of parallel legs 11a and 11bare interconnected at one end through a base portion 12 to form atuning-fork vibrator 13. In the case where the proper vibrationfrequencies of the legs 11a and 11b of the tuning-fork vibrator areequal to each other, no leakage vibration occurs in the base portion 12.Where there is a deviation between these proper vibration frequencies,however, a leakage vibration develops in the base portion 12 andconsequently, if the base portion 12 is supported, the vibrationfrequency of the vibrator varies and its Q is degraded. The propervibration of the legs 11a and 11b can be controlled by reducing theirlengths l₁ and l₂. Accordingly, the vibrator is preformed so that theindividual proper vibration frequencies may each be lower than afrequency desired to obtain, and then the legs are ground to attain thedesired frequency.

FIG. 2 illustrates in a simplified form an apparatus for regulating thevibration frequency of the tuning-fork vibrator according to the presentinvention. The tuning-fork vibrator 13 is mounted on a support 14 andthe support 14 is, in turn, mounted on a base 15 and a control unit andso forth are housed in the base 15. A motor 17 is mounted on an arm 16extended from the base 15 and a grindstone 18 is affixed to the rotaryshaft of the motor 17 so that the legs of the tuning-fork vibrator 13may be ground by the grindstone 18 to adjust their lengths. Thetuning-fork vibrator 13 can be rotated about the center axis between thelegs 11a and 11b to permit grinding of the legs one by one.

The two legs 11a and 11b are each ground by the same length until thevibration frequency of the tuning-fork vibrator 13 becomes higher than areference frequency. The reference frequency is preselected to be lowerthan a desired frequency by a certain value. An oscillation circuit 19which employs, as an element for determining its oscillation frequency,the tuning-fork vibrator 13 is arranged as shown in FIG. 3. Theoscillation frequency of the oscillation circuit 19 is measured by afrequency measuring circuit 21 and the measured value is applied to aregister 22 and then compared by a comparison circuit 24 with thereference frequency set in a register 23. When the oscillation frequencyof the oscillation circuit 19, that is, the vibration frequency of thetuning-fork vibrator 13 becomes equal to or higher than the abovesaidreference frequency, it is detected by the output from the comparisoncircuit 24.

Next, the tuning-fork vibrator 13 is subjected to equilibrium working orstabilization working. More particularly, the tuning-fork vibrator 13 isregulated so that its leakage vibration may be reduced smaller than acertain value. For this regulation, in this example, the tuning-forkvibrator is worked in such a manner as to decrease a difference betweenthe vibration frequency when the base portion 12 of the vibrator 13 ismechanically restrained and the vibration frequency when it is releasedfrom such mechanical restraint. For instance, by urging a clamp ring 26of a collet 25 against the vibrator 13 to clamp its base portion 12 andloosening the clamp, the base portion 12 is mechanically restrained andreleased from the restraint. The clamping by the collet 25 is controlledby a control circuit 27 and, in synchronism with the control, themeasured value obtained by the frequency measuring circuit 21 is appliedto the register 22 and, prior to it, the content of the register 22 istransferred to a register 28.

The contents of the registers 28 and 22 are compared by the comparisoncircuit 29. One of the contents of the registers 22 and 28 is theoscillation frequency of the oscillation circuit 19 when the baseportion 12 of the vibrator 13 is mechanically restrained and the otheris the oscillation frequency when the base portion 12 is not restrainedand a difference therebetween is detected by the comparison circuit 29,the difference output from which is provided via a gate 31 to a displayunit 32. The gate 31 is adapted to be opened by an output which isderived from the comparison circuit 24 when the vibration frequency ofthe vibrator 13 is equal to or higher than the reference frequency, asdescribed previously.

When the difference between the vibration frequency when the restraintis applied and the vibration frequency when the restraint is removed issmaller than a predetermined value, the proper vibration frequencies ofthe legs 11a and 11b become substantially equal and the leakagevibration in the base portion 12 becomes smaller than a predeterminedvalue. Next, the vibration frequency of the vibrator is made to approachthe desired frequency while holding the leakage vibration of the baseportion less than a certain value relative to the legs 11a and 11b.

For example, letting the proper vibration frequency of the vibrator 13at the time of completion of the aforementioned equilibrium working, thedesired vibration frequency and the measured frequency of the vibrator13 be represented by f₀, F₀ and f, respectively, the legs of thevibrator are ground until ##EQU1## becomes sufficiently small in respectof one of the legs and until f₀ -f becomes sufficiently small in respectof the other leg.

Next, a description will be given, with reference to FIG. 4, of a methodfor obtaining, with high accuracy, the proper vibration frequency f₀ ofthe vibrator 13 at the time of completion of the equilibrium working.From a terminal 33 in FIG. 4 is inputted the output electric signal fromthe oscillation circuit 19 which oscillates at a frequency determined bythe crystal vibrator shown in FIG. 3. This signal is converted by ananalog-to-digital converter 34 into a digital signal indicating thatfrequency. The digital signal is applied via a change-over circuit 35 toa register 22 to load therein a free vibration frequency f_(f) at whichthe vibrator oscillates in a free state in which no restraint is imposedon its base portion 12, and thereafter a constrained vibration frequencyf_(c) of the vibrator in the state of its base portion 12 beingmechanically restrained is loaded in a register 28.

A difference between the frequencies stored in these registers 22 and 28is detected by a difference circuit 29 and the difference frequency Δfis stored in a register 36. This Δf is the variation and, in accordancewith the magnitude of the Δf loaded in the register 36, a controlcircuit 37 is controlled and the grinding of the vibrator 13 iscontrolled, for example, by controlling the revolving speed of thegrindstone or its contact pressure and the time of its contact with thevibrator 13 depending on the magnitude of the Δf.

Further, this Δf is compared by a comparator 39 with the previous Δfstored in a register 38. As a result of the comparison of the currentdifference frequency Δf_(n) with the previous difference frequencyΔf_(n-1) loaded in the register 38, if the current difference frequencyΔf_(n) is found to be smaller than the previous difference frequencyΔf_(n-1), the leg of the vibrator being ground currently is furtherground. If the previous difference frequency Δf_(n-1) is smaller thanthe current one Δf_(n), a control circuit 41 is controlled by the outputfrom the comparator 39 to rotate the support of the vibrator 13 and theother leg opposite to the leg currently ground is subjected to grinding.In this way, the Δf is always controlled in a manner to approach aminimum value.

That is, for example, as shown in FIG. 5, each measuring point shiftsalong the curve 42 in the direction of an arrow and the Δf diminishes.Further, the current difference frequency Δf_(n) is compared by acomparator 43 with a set value F₁ from a circuit 44 and when it isdetected that the former is smaller than the latter, a first passcommand is provided to a decision circuit 45.

Moreover, the current difference frequency Δf_(n) in the register 36 isalso supplied to a comparator 46 in which it is compared with the outputΔf_(m) from a minimum value register 47. As a result of this, if theoutput Δf_(n) from the register 36 is smaller than the minimum valueΔf_(m), then a gate 48 is opened by the output from the comparator 46and the Δf_(n) from the register 36 is stored as the Δf_(m) in theminimum value register 47 via the gate 48. If the Δf_(m) is smaller thanthe Δf_(n), then the gate 48 remains closed, retaining the previousminimum value Δf_(m). In this way, a minimum one of the differencefrequencies Δf measured until then is stored as the Δf_(m) in theregister 47.

In an addition circuit 51 a certain value α from a circuit 49 is addedto the Δf_(m) of the minimum value register 47 to provide Δf_(m) +α,which is supplied to a comparator 52 and compared therein with thecurrent difference frequency Δf_(n) from the register 36. When theoutput Δf_(n) from the register 36 is detected to be smaller than Δf_(m)+α, the comparator 52 yields a high-level output.

Further, when the output from the comparator 39 is inverted, the numberof times of inversion is counted by a counting circuit 53. That is, theΔf diminishes along the curve 42 as depicted in FIG. 5, but if grindingis further continued after a minimum value of the curve 42 is reached,then the Δf increases. At this time, the current difference frequencyΔf_(n) from the register 36 becomes larger than the previous differencefrequency Δf_(n-1) from the register 38 and the output from thecomparator 39 is inverted and this is counted by the counter 53 via agate 50.

When the output from the comparator 39 is thus inverted, the leg of thevibrator 13 that is to be ground is switched by the control circuit 41as described previously, so that the measured difference frequency Δfstarts to decrease again, as indicated by the curve 54. In a similarmanner, when the Δf passes through a minimum value of the curve 54 inFIG. 5, the output from the comparator 39 is inverted and this inversionis counted and, at the same time, the leg to be ground is switched.Thereafter, the same operation is repeated.

The number of times of switching between the legs is thus counted andthe count value is compared by a coincidence circuit 56 with apredetermined value, that is, a value N set in a setting circuit 57.When the count value of the counter 53 is N and the output from thecomparator 52 is high-level, the output from a gate 55 becomeshigh-level and this output is applied as a pass command to the decisioncircuit 45 via an OR gate 58.

In this case, an auxiliary reference frequency is provided and after theauxiliary reference frequency is reached, the abovesaid pass command isissued. That is, if the minimum value, namely, the equilibrium state isdetected at a frequency appreciably lower than the vibration frequencyF_(o) which it is desired to obtain, then grinding of both legs by thesame amount until the desired frequency is reached from that detectedfrequency introduces the possibility that the equilibrium between thetwo legs will be destroyed during the grinding. To avoid this, theminimum value, that is, the equilibrium state is detected after theauxiliary reference frequency is reached.

To this end, the auxiliary reference frequency F_(a) is stored in aregister 59 and this frequency is compared by a comparison circuit 61with the frequency f_(f) from the register 22 which is the frequencywhen the base portion is not restrained. In the case where the frequencyf_(f) of the vibrator to be regulated does not reach the auxiliaryreference frequency F_(a), the control circuit 37 is controlled by theoutput from the comparison circuit 61 to effect grinding of thevibrator.

When the frequency f_(f) of the crystal vibrator with no restraintimposed on its base portion becomes higher than or equal to theauxiliary reference frequency F_(a), the output from the comparisoncircuit 61 is inverted to a high-level output, by which an AND gate 62is opened to detect coincidence with the output from the control circuit37 and it is counted by a binary counter 63. When the counter 63 counts2 in this state, its output inverts a flip-flop 64, by the output fromwhich the AND gate 50 is opened. From this state, counting of theinversion of the output from the comparator 39 by the counter 53 isstarted.

If an extremely small Δf is obtained by a first measurement, then ithappens that no Δf smaller than the Δf_(m) +α can be obtained in theregister 36 in the subsequent measurements and the output from thecomparator 52 does not become high-level. In other words, no passcommands can be yielded. To avoid this, a value M set in a settingcircuit 65 and the count value of the counter 53 are compared by acoincidence detection circuit 66 and, in the case of coincidence, a passcommand is applied by its output to the decision circuit 45 via the ORgate 58.

The output from the comparator 39 is also supplied to the decisioncircuit 45 and in the case where the current measured value Δf_(n) fromthe register 36 is larger than the previous measured value Δf_(n-1), itis rejected even if other conditions are fulfilled. That is, any one ofor a combination of the facts that the Δf is smaller than the fixedvalue F₁ in the comparator 43, that the count value of the counter 53coincides with the set value N, and that the count value of the counter53 coincides with the set value M, is decided to be acceptable as apass, but when it is detected by the comparator 39 that the currentmeasured value Δf_(n) is larger than the previous measured valueΔf_(n-1), it is decided to be rejected.

It is also possible to omit the counter 53 and make a pass decision inthe state in which the output from the comparator 52 is obtained, but insuch a case it is necessary to satisfy the requirement at the output ofthe comparator 43 and the requirement in the comparator 39 that thecurrent measured value is smaller than the previous one.

In this way, the variation, that is, the minimum value of the differenceΔf between the frequencies when the base portion of the vibrator isrestrained and when it is not restrained, is detected. Then, the crystalvibrator is ground to reach the desired frequency F_(o) while retainingthe difference frequency without substantial change. To accomplish this,the free vibration frequency when the base portion is not restrained inthe case of the variation being decided as minimum is set as f_(o) inthe register 60 from the register 22. The desired frequency F_(o)prestored in a setting circuit 23 and the frequency f_(o) are averagedby an averaging circuit 69; namely, ##EQU2## is calculated.

To a switching circuit 70 are applied the outputs F_(o) ' from theaveraging circuit 69 and F_(o) from the setting circuit 23 and, atfirst, the averaged value output F_(o) ' is supplied to a subtractioncircuit 171, wherein there is calculated a difference, F_(o) '-f_(f),between it and the output measured when the base portion was notrestrained, that is, the output f_(f) from the register 22. Inaccordance with the subtracted output, the control circuit 37 iscontrolled, effecting control of grinding of the vibrator.

The output from the subtraction circuit 171 is compared by a comparator172 with a reference value F₂ from a circuit 173 and when the former issmaller than the value F₂ the control circuit 41 is controlled by theoutput from the comparator 172 to control the switching circuit 70 andthe target value F_(o) is derived as the output therefrom and adifference between it and the f_(f) from the register 22 is detected bythe circuit 171. This output and a reference value F₃ from a circuit 174are compared in a comparison circuit 67 and when the output from thedifference circuit 171 becomes smaller than the reference value F₃, acontrol circuit 68 is controlled by the output from the comparisoncircuit 67, putting an end to the overall process.

Since the regulation and control for preventing the variation fromsubstantial fluctuation are always repeated, even if the region of aminimum value of the variation is narrow, a correct minimum value can bedetected in a short time.

Further, not only the variation below a certain value is decided as aminimum value but also it is decided that the variation has passedthrough the minimum value and, in addition, the minimum value is used asa reference, so that even in the case of scattered minimum valuecharacteristics, the variation can always be regulated to the minimumvalue. In the case where it is checked, before regulation to the minimumvalue, whether the auxiliary reference value F_(a) has been reached ornot and the vibrator is worked to the value F_(a) close to the targetvalue first and then the minimum value is detected, as in the aboveembodiment, the regulation after the minimum value is reached, that is,the working time for approaching the target value after both legs areequilibrated is short and the amount of working is also small and theminimum value of the variation is not likely to undergo substantialchanges. Moreover, the control for adjusting the variation to theminimum value and the control for adjustment to the target value afterthe minimum value is reached may be arranged entirely separately of eachother. Besides, the difference between the vibration frequencies in thecases of the base portion of the tuning-fork vibrator being restrainedand not restrained is used as the variation, but it is also possible todetect, as the variation, the magnitude of the leakage vibration of thebase portion.

Grinding apparatus for grinding the crystal vibrator to regulate it forbalancing its legs can be constituted, for example, by the followingarrangement.

As shown in FIG. 6, a rotary box 71 is rotatably mounted on a base 15.On both end portions of the rotary box 71 are respectively providedworkpiece holding mechanisms 72 (one of which is not seen in FIG. 6) anda sound insulating cover 73 for noise insulation, which covers theholding mechanism 72, can be mounted on the rotary box 71. A panel 74 isprovided on an extension part which extends from the base 15 to lieabove the rotary box 71. On the panel 74 on the side of the base 15 ispositioned that one of the holding mechanisms (which is not seen in thedrawing) and a grindstone employed as a tool is dispersed opposite aworkpiece held by that holding mechanism, that is, a vibrator, thoughnot shown, and a motor 17 for rotating the grindstone is provided on theextension part of the base 15 on the opposite side from the part.Further, the holding mechanisms 72 and the rotary box 71 projecting fromthe panel 74 can be covered with a panel cover 75, as required.

The rotary box 71 is affixed to a rotary support shaft 76 which isrotatably supported to project upwardly from the base 15, as depicted inFIG. 7. A motor 78 in the base 15 and the support shaft 76 are coupledby a chain 79 to rotate the rotary box 71 by driving of the motor 78.

An inclined base plate 81, which is inclined, for instance, at an angleof 45°, extends from the base 15 obliquely above the rotary box 71 and ashaft 82 is passed through the inclined base plate 81 substantially atright angles thereto and a diamond wheel, that is, the grindstone 18 ismounted at one end of the shaft 82 on the side of the rotary box 71. Theother end of the shaft 82 is coupled with the rotary shaft of the motor17.

This example is arranged so that as the grindstone 18 rotates, thegrindstone 18 is reciprocated in a direction perpendicular to its rotaryshaft. That is, as shown in FIGS. 7 and 8, a gear 83 is formed on theshaft 82 and a gear 84 is meshed with the gear 83 and, as shown in FIG.8, a cam groove 86 which is oblique to a shaft 85 of the gear 84 isformed in the peripheral surface of one end portion of the shaft. In thecam groove 86 is inserted a pin 87 which is fixed to the inclined baseplate 81.

The shaft 85 is rotatably held in a gear box 88 and the motor 17 isfixed to the gear box 88 and the gear box 88 is adapted to be guided bya pair of guide shafts 89 and 91 provided on the inclined base plate 81so that it moves along the inclined base plate 81. By the rotation ofthe motor 17, the cam 86 is rotated through the gears 83 and 84 andsince the pin 87 is fixed, the cam shaft 85 moves in its axial directionand consequently the gear box 88 and the motor 17 are guided by theguide shafts 89 and 91 to move. That is, the shaft is reciprocated bythe rotation of the cam groove 86.

The workpiece holding mechanism 72 consists of two mechanisms 72a and72b and, as shown in FIG. 11 with respect to the mechanism 72a, a holder92 partly projects out from a hole 93 of a top panel of the rotary box71 and the holder 92 is supported in a manner to be rotatable about ashaft 94 provided in the rotary box 71. At the inner end of the holder92 a projecting piece 95 projects towards the base 15 and the projectingpiece 95 is held between the end face of a stopper 97 attached to a sidepanel 96 of the rotary box 71 and a movable stopper 98.

In the holder 92 is incorporated a motor, though not shown, and itsmotor shaft 90 projects towards the inclined base plate and a tubularmember 99 is mounted on that motor shaft 90 to extend therefrom so thatit makes rotary engagement therewith and is slidable thereon in itsaxial direction. On the outside of the tubular member 99 are disposed aplurality of collet pawls 101 and these collet pawls 101 are positionedso that they can hold, for example, the base portion 12 of thetuning-fork vibrator 13, disposed therebetween. The collet pawls 101 areattached to one end of a springy support piece 102 and the other end ofthe support piece 102 is fixed to a base 103. Due to its springyproperty the support piece 102 biases the collet pawls 101 outwardly ofeach other, that is, in a direction in which they deviate from the baseportion 12. The outer surfaces of the collet pawls 101 are tapered toturn away outwardly from each other as the upper side of the vibrator 13is approached. The upper end portion of the tubular member 99 forms aholding member 100 and the vibrator 13 is held by the holding member100. That is, for example, as shown in FIG. 12, conducting pipes 114 and115 are buried in the holding member 100 to extend from its end face inits axial direction and the vibrator 13 is held by the holding member100, with leads 116 and 117 led out from the bottom of the base portion12 of the vibrator being inserted into the pipes 114 and 115. It isdesirable that a leak preventive layer 118 as of silicone rubber forpreventing sound leakage is mounted on the vibrator holding surface ofthe holding member 100. The mounting of the holding member 100 will bedescribed later.

In FIG. 11, on the outside of the collet pawls 101 is disposed coaxiallytherewith a clamp ring 104. The clamp ring 104 is formed on a movablecylinder 105 as a unitary structure therewith in the shape of a flangeon the inside thereof. The inner surface of the ring is tapered so thatits diameter decreases as it goes away from the vibrator 13 and thissurface is adapted to match with the tapered outer surfaces of the pawls101.

In the movable cylinder 105 a coiled spring 106 is wound around thesupport piece 102 between the clamp ring 104 and the base 103 and, bythe coiled spring 106, the clamp ring 104 is biased towards the vibrator13, that is, upwardly in FIG. 11, by which the collet pawls 101 areurged inwardly to press the outer peripheral surface of the base portion12 substantially uniformly by the inner surfaces of the pawls 101.

In this way, a force can be applied to the base portion 12 uniformlysubstantially all over the outer peripheral surface thereof. On theoutside of the other end of the movable cylinder 105 is formedintegrally therewith an engaging flange 107 and a drive ring 108 isdisposed coaxially with the flange 107 in opposing relation thereto onthe side of the collet pawls 101. The drive ring 108 is attached to oneend of a drive cylinder 109 and a marginal flange 111 is formed as aunitary structure with the other end of the drive cylinder 109. Thedrive cylinder 109 is movably engaged with the holder 92 coaxiallytherewith. A marginal flange 112 on the bottom end of the holder 92 isdisposed in opposing relation to the marginal flange 111. Between themarginal flanges 111 and 112 a coiled spring 113 is wound around theholder 92 and the marginal flange 111 is biased by the spring 113towards the side of the collet pawls 101. Accordingly, the drive ring108 is disengaged from the engaging flange 107 and the movable cylinder105 is moved by the action of the spring 106 towards the side of thecollet pawls 101 and, as a result, the collet pawls 101 are clamped bythe clamp ring 104.

When the drive cylinder 109 is pressed down by the marginal flange 111against the biasing force of the coiled spring 113 to approach the sideof the marginal flange 112, the drive ring 108 engages with the engagingflange 107 to pull down the movable cylinder 105 to withdraw it from thecollet pawls 101 and the collet pawls 101 are opened by the springaction of the support piece 102 to release the base portion 12 of thevibrator 13 from the restraint thereon.

The base portion 12 of the vibrator is fixed to the holder 92 and thetubular member 99 of the holding member 100 is inserted into a centralhole of the base 103. The lower half portion of the inner peripheralsurface of the base 103 is increased in diameter to form a steppedportion 119 and the outer diameter of the tubular member 99 below thestepped portion 119 is increased to form another stepped portion 121.Between these stepped portions 119 and 121 a coiled spring 122 is woundaround the tubular member 99 and the holding member 100 is biaseddownwardly by the action of the spring 122.

Further, a rotary shaft 123 is provided in a lateral hole made in theintermediate portion of the base 103 and a rotary lever 124 is mountedon the shaft 123. One end of the rotary lever 124 is inserted into ahole made in the tubular member 99 to engage therewith. The other end ofthe rotary lever 124 projects out from a hole 125 of the movablecylinder 105.

In the case where the movable cylinder 105 has been moved by a distancenecessary for merely removing the restraint imposed on the base portion12 by the collet pawls 101, the rotary lever 124 does not engage withthe top end of the hole 125. When the movable cylinder 105 has beenfurther pulled down towards the holder 92, however, the rotary lever 124engages with the top end of the hole 125 and the rotary lever 124rotates anticlockwise in the drawing, by which the holding member 100moves away from the holder 92 and the base portion 12 projects upwardlyof the collet pawls 101, permitting the tuning-fork vibrator 13 to bedismounted easily.

An elongated hole 126 is made in the movable cylinder 105 to extend inits axial direction and a stopper pin 127 fixed to the peripheralsurface of the base 103 projects out from the elongated hole 126. By thepin 127 and the elongated hole 126 is limited the range of movement ofthe movable cylinder 105.

A contact mechanism is provided by which the vibrator 13 held by theholding structure is brought into contact with the grindstone 18. Adamper mechanism is additionally provided for alleviating shockresulting from the contact. That is, as depicted in FIG. 11, in therotary box 71 the projecting piece 95 projecting from the holder 92towards the base 15 is coupled with a plunger 129 of a plunger solenoid128. The projecting piece 95 is fixed to the plunger 129 and aresistance plate 131 is fixed to an extension of the projecting piece.The resistance plate 131 is inserted into a body of damper oil, forexample, silicone oil 133 which is housed in a container 132 mounted inthe rotary box 71.

The movable stopper 98 is coupled with one end of a rotary arm 134 andthe rotary arm 134 projects out from a bottom panel of the rotary box 71and is adapted to be rotatable about a shaft 135. At the position of theshaft 135 the rotary arm 134 is bent and when its bend portion 134a isrotated clockwise in FIG. 11, the rotary arm 134 rotates to withdraw themovable stopper 98 from the projecting piece 95. Accordingly, uponenergization of the plunger solenoid 128 in that state, the plunger 129moves back to rotate the motor holder 92 about the shaft 94 and, as aresult of this, the vibrator 13 is brought into contact with thegrindstone 18.

This contact is gradually made without shock through the action of theresistance plate 131 and the damper oil 133. By aligning the center linebetween the two legs of the vibrator 13 held by the holding member 100with the axis of the shaft 90 of the motor disposed in the holder and byrotating the motor shaft 90 through 180°, both legs of the vibrator 13can be contacted with the grindstone 18 under the same condition andboth legs can be ground by the same amount. When the rotary box 71 isrotated to place the vibrator 13 opposite the grindstone 18, the bentportion 134a of the rotary arm 134 corresponding to the holdingstructure 72a holding the vibrator 13 engages with a projection 136fixed on the base 15 to perform the clockwise rotation. In connectionwith the rotary arm 134 for the holding mechanism 72b which is notengaged with the grindstone 18, however, such projection 136 is notprovided on the base 15 opposite the bent portion 134a. Accordingly,this holding structure 72b is held stably by the stoppers 97 and 98. Inorder that the movable stopper 98 may automatically be restored, acoiled spring 137 is provided between the rotary arm 134 and aprojection mounted on the bottom panel of the rotary box 71, as shown onthe side of the holding structure 72b in the drawing, by which therotary arm 134 is automatically restored.

The drive cylindrical member 109 is biased by the spring 113 upwardly ofthe holder 92, that is, in the direction in which it projects out fromthe rotary box 71. Accordingly, the drive cylindrical member 109 ispushed up and the drive ring 108 also lies in its raised position toclamp the collet pawls 101 by the action of the spring 106.

As depicted in FIG. 10, in the rotary box 71 an intermediate portion ofa press lever 138 is rotatably attached to its top panel and one endportion of the lever is disposed opposite the upper surface of theflange 111 of the drive cylindrical member 109. A push rod 141 projectsout from the bottom panel of the rotary box 71, guided by a guide member139 in a manner to be movable up and down, and the other end portion ofthe press lever 137 is positioned above the upper end of the push rod141. To the lower end of the push rod 141 is rotatably attached a roller142.

In the holding mechanism 72b which is not disposed opposite thegrindstone 18, as shown in FIG. 11, the roller 142 rides on a relativelylarge projection of the base 15. Consequently, the push rod 141 moves upto rotate the press lever 138 counterclockwise in FIG. 10, by which theflange 111 is greatly pressed down to pull down the drive cylindricalmember 109. In consequence, as described previously, the movablecylinder 105 is also greatly pushed down to release the clamping of thecollet pawls 101 and, at the same time, the tubular member 99 and theholding member 100 are pushed up, permitting easy removal of thevibrator 13. In the holding mechanism 72a disposed opposite thegrindstone 18, however, since the projection on which the roller 142runs is lower than that on the side of the holding mechanism 72b, it ispossible to achieve only the control for opening and closing the colletpawls 101 without rotating the rotary lever 124.

For the regulation of the vibrator, it is necessary to know which one ofthe legs 11a and 11b is higher in proper vibration. To this end, asdepicted in FIG. 13, a tungsten lamp or the like is used as a lightsource 146 and light from the light source 146 is rendered by a lens 147into parallel rays and applied to the vibrator 13 at right angles to thedirection of elongation of the legs 11a and 11b. A light shield plate148 is disposed on the opposite side from the light source 146 withrespect to the vibrator 13, the light shield plate 148 having formedtherein a slit 149. The slit 149 and the legs 11a and 11b of thevibrator bear a relationship such as shown in FIG. 14, wherein when theyare viewed from the direction perpendicular to the direction ofelongation of the legs, they overlap and in the case where the vibrator13 is vibrated by an exciter 151, when the legs 11a and 11b are close toeach other, transmitted light passing through the slit 149 decreases,whereas when the legs 11a and 11b are opened relative to each other, thetransmitted light increases. In this way, the amount of lighttransmitted through the slit 149 varies in accordance with theopen-close vibration of the legs 11a and 11b. The light having passedthrough the slit 149 is received by a photoelectric conversion element152 for conversion into an electric signal. As the photoelectricconversion element 152, use can be made of, for instance, a phototransistor and its emitter side is grounded via a resistor 153 and thecollector side is connected via a resistor 154 to a power sourceterminal 155 and, at the same time, the DC component is cut off by acapacitor 156 to take out only the AC component. That is, an ACoscillation representative of the open-close vibration of the legs 11aand 11b is taken out.

This electric signal of the open-close vibration is amplified by anamplifier 157 and, further, unnecessary components are removed by afilter 158 to take out the open-close vibration component alone, whichis supplied to a phase comparator 159. On the other hand, apiezo-electric element 161, for instance, is mounted on one side of thelegs 11a and 11b adjacent the base portion 12 of the vibrator 13, bywhich an unbalanced vibration of the base portion of the vibrator 13 isdetected as an electric signal. This detected output is provided via anamplifier 162 to the phase comparator 159, wherein it is phase-comparedwith the open-close vibration from the amplifier 157. A phase adjuster163, which is inserted in one of the two signal paths, is adjusted sothat the phase difference between the open-close vibration and theunbalanced vibration, which are detected regardless of measurementerrors and the characteristics of the amplifiers 157 and 162, may be inphase or out of phase with each other.

It is already known that when the comparison result of the phasecomparator 159 is in-phase, the proper vibration of the leg, forinstance, 11b is higher in frequency than the proper vibration of theleg 11a, whereas in the case of the comparison result beingout-of-phase, the proper vibration of the leg 11b is lower in frequency.Accordingly, the output from the phase comparator 159 can be used todetect which one of the legs 11a and 11b is higher in the propervibration frequency than the other. It is possible to similarly detectwhich one of the legs is higher or lower in the proper vibrationfrequency than the other in a magneto-strictive tuning-fork vibrator aswell as in a piezo-electric vibrator. In this way, it can be detected,without working the legs of the vibrator, which one of them is higher inthe proper vibration frequency than the other.

We claim:
 1. A method for frequency regulating a two-legged tuning-fork vibrator, comprising a first step of working said tuning-fork vibrator so that its vibration frequency becomes higher than a reference frequency which is lower than a desired frequency by a predetermined value; a second step of detecting a difference between a constrained vibration frequency produced by the vibrator when a mechanical restraint is imposed on a base portion of said tuning-fork vibrator and a free vibration frequency produced when the restraint is removed, and working said tuning-fork vibrator so as to reduce said difference; and a third step of working said tuning-fork vibrator so that its vibration frequency reaches said desired frequency, while said difference between said constrained and free vibration frequencies is maintained at a value smaller than a certain value.
 2. A method for frequency regulating a tuning-fork vibrator according to claim 1 wherein, in said second step, said difference between the free vibration frequency and the constrained vibration frequency of the tuning-fork vibrator is measured for each working of one of the legs; said measured value is compared with a previous such measured value; when the currently measured value is smaller than the previously measured value, the leg being worked is further worked and when the currently measured value is larger than the previously measured value, the other leg is worked; the same operations are repeated; and when it is detected that said difference has become smaller than a predetermined value, the second step is terminated.
 3. A method for frequency regulating a tuning-fork vibrator according to claim 1 wherein, in said second step, said difference between the free vibration frequency and the constrained vibration frequency of the tuning-fork vibrator is measured for each working of one of the legs; said measured value is compared with a previous such measured value; when the currently measured value is smaller than the previously measured value, the leg being worked is further worked and when the currently measured value is larger than the previously measured value, the other leg is worked; the same operations are repeated; and when a minimum value of said difference in the proper vibration frequency is detected, the second step is terminated.
 4. A method for frequency regulating a tuning-fork vibrator according to claim 3 wherein the number of times of switching the working between the legs is counted and after the count value has become larger than a first predetermined value, the second step is terminated when the abovesaid minimum value is detected.
 5. A method for frequency regulating a tuning-fork vibrator according to claim 4 wherein in the case where the abovesaid minimum value is not detected, the second step is terminated when it is detected that the said count value has become larger than a second predetermined value which is larger than the said first predetermined value.
 6. A method for frequency regulating a tuning-fork vibrator according to claim 1 wherein, in said second step, said difference between the free vibration frequency and the constrained vibration frequency of the tuning-fork vibrator is measured for each working of one of the legs; said measured value is compared with a previous such measured value; when the currently measured value is smaller than the previously measured value, the leg being worked is further worked and when the currently measured value is larger than the previously measured value, the other leg is worked; the same operations are repeated; the number of times of switching the working between the legs is counted; and when it is detected that the count value has become larger than a predetermined value, the second step is terminated.
 7. A method for frequency regulating a tuning-fork vibrator according to any one of claims 2, 3, 5 or 6 wherein when the current measured value is larger than the previous one, the second step is not terminated.
 8. A method for frequency regulating a tuning-fork vibrator according to claim 1 wherein in said second step, said difference between the free vibration frequency and the constrained vibration frequency of the tuning-fork vibrator is measured for each working of one of the legs; said measured value is compared with a previous such measured value; when the currently measured value is smaller than the previously measured value the leg being worked is further worked and when the currently measured value is larger than the previously measured value the other leg is worked; the same operations are repeated; and when both said difference becomes smaller than a predetermined value and a minimum value of said difference is detected, said second step is terminated.
 9. A method for frequency regulating a tuning-fork vibrator according to claim 4 wherein when the currently measured value is larger than the previously measured value, said second step is continued.
 10. A method for frequency regulating a tuning-fork vibrator according to any one of claims 2, 3, 5, 6, 1, 8 or 9 wherein the third step consists of obtaining an average value of the desired frequency and the vibration frequency produced by the tuning-fork vibrator when said second step is completed; working the tuning-fork vibrator in accordance with the difference between said average value and the vibration frequency of the tuning-fork vibrator so that the difference may be reduced; detecting that the difference between the average value and the vibration frequency of the tuning-fork vibrator has become smaller than a predetermined value; working the tuning-fork vibrator in accordance with the difference between the vibration frequency of the tuning-fork vibrator and the said desired frequency so that the difference may be reduced, and terminating the third step when it is detected that the difference has become smaller than a predetermined value.
 11. A method for frequency regulating a tuning-fork vibrator according to any one of claims 2, 3, 5, 6, 1, 8 or 9, characterized in that when the working in the first or second step is started, an open-close vibration between the two legs of the tuning-fork vibrator and an unbalanced vibration of the tuning-fork vibrator are respectively detected; determining whether both vibrations are of the same phase or opposite phases; and based on said determination, determining which of the legs of the tuning-fork vibrator should be worked first. 